Safety braking apparatus for portable chain saw

Abstract

A chain saw having an improved safety brake actuating mechanism is disclosed. The actuating mechanism includes a safety lever pivotally mounted on the chain saw housing for movement from an operating position to a braking position in which a brake band is brought into frictional engagement with motive means which drives a cutting chain. A latching member is pivotally mounted on the safety lever for releasable latching engagement with the housing. A spring member engaged intermediate the housing and the latching member exerts a yieldable force on the safety lever which constantly biases the safety lever for movement from the operating position to the braking position while also exerting a yielding latching force on the latching member. The spring member cooperates with the safety lever for holding the latching member in releasable latching engagement with the housing and for resisting movement of the safety lever thereby preventing inadvertent frictional engagement of the brake band with the motive means when the lever is in the operating position. The spring member is cooperatively engaged with the safety lever for permitting rotation and disengagement of the latching member from the housing as the safety lever rotates from the operating position to the braking position in response to an actuating force acting on the safety lever.

I claim: 
     
       1. In a chain saw of the type including a housing, a guide bar projecting from said housing, a cutting chain mounted to run on said guide bar, and motive means carried by said housing coupled to said cutting chain for propelling said cutting chain around said guide bar, the improvement comprising, in combination: a safety lever pivotally mounted on said housing for movement from an operating position to a braking position;   a brake band having a first end portion coupled to said safety lever, a second end portion coupled to said housing, and an intermediate portion disposed for frictional engagement with said motive means in response to movement of said safety lever from said operating position to said braking position;   a latching member pivotally mounted on said safety lever for rotational movement relative to said force transmitting safety lever, said latching member having a first end portion disposed for releasable engagement with said safety lever and a second end portion disposed in releasably latching engagement with said housing; and,   a spring member engaged intermediate said housing and said latching member, said spring member exerting a yieldable force on said safety lever which constantly biases said safety lever for movement from said operating position to said braking position, said spring member also exerting a yieldable latching force on said latching member and cooperating with said safety lever for holding said second end portion of said latching member in releasably latching engagement with said housing for resisting movement of said safety lever and thereby preventing inadvertent frictional engagement of said brake band with said motive means when said safety lever is in said operating position, and said spring member cooperating with said safety lever for permitting rotation and disengagement of said latching member from said housing as said safety lever rotates from said operating position to said braking position in response to an external actuating force acting on said safety lever.   
     
     
       2. The chain saw combination as defined in claim 1, said spring member comprising a lineally acting coil spring compressively seated intermediate said housing and said latching member, said lineally acting coil spring having a first end portion engaging said first end portion of said latching member and a second end portion engaging said housing. 
     
     
       3. The chain saw combination as defined in claim 1, said spring member comprising a lineally acting coil spring compressively seated intermediate said housing and said latching member, the first end of said brake band being enclosed by and extending through said lineally acting coil spring. 
     
     
       4. The chain saw combination as defined in claim 1, said first end of said brake band being bifurcated thereby defining a central passage, the first end portion of said latching member projecting through said central passage and engaging said safety lever. 
     
     
       5. The chain saw combination as defined in claim 4, said safety lever having a recess receiving the bifurcated end portions of said brake band and an anchor pin bridging said recess, said bifurcated end portions of said brake band being secured to said anchor pin. 
     
     
       6. The chain saw combination as defined in claim 1, said safety lever having a pin projecting orthogonally with respect to said safety lever, said latching member being mounted on said pin for rotational movement of said first and second end portions relative to said safety lever. 
     
     
       7. The chain saw combination as defined in claim 1, said housing having a latch pin and a roller carried by said latch pin for engaging the second end portion of said latching member. 
     
     
       8. The chain saw combination as defined in claim 1, said latching member comprising a central body portion pivotally mounted on said safety lever, said first and second end portions projecting from said central body portion in substantially orthogonal relation relative to each other, said first end portion defining a lever arm for engaging said spring member and transmitting the yieldable latching force exerted by said spring, and said second end portion having a detented surface for engaging said housing. 
     
     
       9. The chain saw combination as defined in claim 8, said housing having a latch pin and a roller carried by said latch pin for releasably engaging said detented surface of the second end portion of said latching member, and said second end portion having an inclined surface for engaging said roller as said latching member rotates relative to said safety lever. 
     
     
       10. In a chain saw of the type including a housing, a guide bar projecting from said housing, a cutting chain mounted to run on said guide bar, and motive means carried by said housing coupled to said cutting chain for propelling said cutting chain around said guide bar, the improvement comprising, in combination: a safety lever pivotaly mounted on said housing for movement from an operating position to a braking position;   a brake band having a first end portion coupled to said safety lever, a second end portion coupled to said housing, and an intermediate portion disposed for frictional engagement with said motive means in response to movement of said safety lever from said operating position to said braking position;   a latching member pivotally mounted on said safety lever for rotational movement relative to said force transmitting safety lever, said latching member having a first end portion disposed in releasably latching engagement with said housing and having a second end portion defining a moment arm relative to the pivotal axis of said latching member for transmitting a latching force to said first end portion and to said safety lever; and,   a spring member engaged intermediate said housing and said latching member, said spring member exerting a yieldable force on said safety lever which constantly biases said safety lever for movement from said operating position to said braking position, said spring member also exerting a yieldable latching force on said latching member and cooperating with said safety lever for holding said second end portion of said latching member in releasably latching engagement with said housing for resisting movement of said safety lever and thereby preventing inadvertent frictional engagement of said brake band with said motive means when said safety lever is in said operating position, and said spring member cooperating with said safety lever for permitting rotation and disengagement of said latching member from said housing as said safety lever rotates from said operating position to said braking position in response to an external actuating force acting on said safety lever.   
     
     
       11. The chain saw combination as defined in claim 10, said spring member comprising a torsion spring having a first end portion coupled to said latching member and a second end portion coupled to said housing. 
     
     
       12. The chain saw combination as defined in claim 11, said torsion spring being mounted in coaxial relation with the pivotal axis of said safety lever. 
     
     
       13. The chain saw combination as defined in claim 11, said safety lever being pivotally mounted to said housing by means of a pivot pin projecting intermediate said housing and said safety lever, said torsion spring being mounted in coaxial relation with and enclosing said pivot pin. 
     
     
       14. The chain saw combination as defined in claim 11, said latching member being pivotally mounted to said safety lever by means of a pivot pin projecting intermediate said latching member and said safety lever, the first end portion of said torsion spring being coupled to the moment arm portion of said latching member at a point opposite the longitudinal centerline of said pivot pin.